Method of chemically polishing nickel



"surfaces at room temperature.

Patented June 8, 1954 Leonard P.- Fox; Lancaster; Pa -assigned to Radio i Corporation. of America; a corporation of- Delaware No Drawing. Application April 1, 1952,

"Serial No.-"279,'955

7 Claims.

This invention relates to chemical polishing of nickel surfaces and, more particularly, to a method of chemically polishing nickel surfaces at ordinary room temperatures.

Although many types of baths have previously been proposed for chemically polishing nickel surfaces, these have generally required the use of elevated temperatures. This usually results in undesirable fuming, with accompanying health hazards, and also, of course, increases the cost of treatment. Polishing of nickel surfaces has also been carried out by electrolytic methods. Since this involves the expenditure of considerable electrical energy, the cost of this type of treatment is inherently greater than that for a treatment which does not involve passage of electric current through a solution.

The present invention resides in the use of a particular bath for chemically polishing nickel surfaces, which is rapid in treatment and completely effective at ordinary room temperatures. The bath comprises 60-70% by volume glacial acetic acid, 40-30% by volume concentrated nitric acid, and about 0.5 cc. concentrated hydrochloric acid per 100 cc. of solution. Depending upon the initial surface condition of the metal, treatment is accomplished by immersing the nickel part to be polished in the bath for at least seconds.

Baths comprising nitric acid, acetic acid and small amounts of hydrochloric acid have previously been proposed for chemically polishing nickel alloys such as Monel metal. For example, it has previously been proposed to polish Monel metal, using a bath containing 50% concentrated nitric acid, 50% glacial acetic acid, and 0.25% hydrochloric acid. This bath was operated at a temperature of 135 F. Although this bath also produces fairly good polishing results on nickel at elevated temperatures of, say 135 F., it produces practically no polishing effect on nickel Unexpectedly, it was found that bychanging the proportions of the nitric and acetic acid to those above mentioned, a very much greater polishing effect was obtained on nickel at ordinary room temperatures. The proportions of all ingredients are critical.

The objects of the present invention are to provide a bath that will give improved chemical polishing of nickel surfaces at room temperatures, and to provide an improved process of nickel polishing that does not require the passage of electrical current or use of elevated temperatures.

These; and (other objects will be more apparent and the invention willb'e more readily understood from" the following detailed description of preferred examples:

Example I A bath was made up consisting essentially of: Percentage by volume Glacial acetic acid Concentrated nitric acid (specific gravity Concentrated hydrochloric acid (specific gravity 1.19) 0.5 cc. per cc. of solution The article having the nickel surface to be polished is treated, preferably, by immersing in the above solution for at least 15 seconds and, for best results, for about 30 seconds, although the exact time of treatment that should be used depends upon the initial surface condition of the metal.

Before a nickel surfaced article can be polished as above described, it should first be cleaned to remove the surface film of oxide. This can be done in any one of many well known ways. A preferred method is to prepare a solution containing 30 gms. of cupric chloride and 500 cc. concentrated hydrochloric acid in 1,000 cc. of water. This bath is maintained at about F. and the article is cleaned by immersion in the bath for at least about 5 minutes. Within a few hours after cleaning, the part to be polished should be immersed in the polishing bath.

The proportions of ingredients in the preferred example of polishing bath, given above, cannot be varied to any great extent without destroying the effectiveness of the polishing action. However, the glacial acetic acid content may be varied between 60-70% by volume and the concentrated nitric acid can then be varied between 40-30 by volume. The amount of concentrated hydrochloric acid cannot be changed to any extent. If the amount used is appreciably less than 0.5 cc. per 100 cc. of solution, the polishing action becomes rapidly slower, and vanishes entirely if no hydrochloric acid is used in the bath. If substantially more than 0.5 cc. per 100 cc. of solution is used, the polishing action becomes slower instead of more rapid and effectiveness of the bath at room temperature largely disappears. a

The time of treatment is not particularly criti cal, although it is preferable that the article be left in the polishing bath at least 30 seconds. The time varies with initial surface condition and can be much longer without destroying the polish. However, if more time is used, nickel dissolves in the bath and there is no increase in degree of polish. Consequently, it is preferable to use as short a time as will give the desired degree of polish.

I claim:

1. A bath for use in chemically polishing nickel surfaces consisting of 60-70% by volume glacial acetic acid, 40-30% by volume concentrated nitric acid, and about 0.5 cc. concentrated hydrochloric acid per 100 cc. of solution.

2. A bath according to claim 1 in which the amount of glacial acetic acid is 60% by volume, and the amount of concentrated nitric acid is 40% by volume.

3. A method of chemically polishing a nickel surface comprising treating said surface, in cleaned condition, at room temperature with a solution consisting of 60-70% by volume glacial acetic acid, -30% by volume concentrated nitric acid, and about 0.5 cc. concentrated hydrochloric acid acid per 100 cc. of solution.

4. A method according to claim 3 in which the bath contains glacial acetic acid by volume, and 40% concentrated nitric acid by volume.

5. A method according to claim 3 in which the time of treatment is at least 15 seconds.

6. A method according to claim 5 in which the time of treatment is about 30 seconds.

7. A method of chemically polishing a nickel surface comprising cleaning the oxide film from said surface and treating the cleaned surface at room temperature with a solution consisting of 60-70% by volume glacial acetic acid, 40-30% by volume concentrated nitric acid, and about 0.5 cc. concentrated hydrochloric acid per cc. of solution.

References Cited in the file of this patent UNITED STATES PATENTS Number w unm- 

3. A METHOD OF CHEMICALLY POLISHING A NICKEL SURFACE COMPRISING TREATING SAID SURFACE, IN CLEANED CONDITION, AT ROOM TEMPERATURE WITH A SOLUTION CONSISTING OF 60-70% BY VOLUME GLACIAL ACETIC ACID, 40-30% BY VOLUME CONCENTRATED NITRIC ACID, AND ABOUT 0.5 CC. CONCENTRATED HYDROCHLORIC ACID ACID PER 100 CC. OF SOLUTION. 